docs + fixed warnings

fyrox-impl/src/renderer/ui_renderer.rs

@@ -96,11 +96,19 @@ pub struct UiRenderContext<'a, 'b, 'c> {
     pub resource_manager: &'a ResourceManager,
 }
 
+/// Contains all the info required to render a user interface.
 pub struct UiRenderInfo<'a> {
+    /// A render target to render a user interface (UI) to. If [`None`], then the UI will be rendered
+    /// to the screen directly.
     pub render_target: Option<TextureResource>,
+    /// Screen size for the UI. In most cases, it should be `ui.screen_size()`.
     pub screen_size: Vector2<f32>,
+    /// A drawing content of a UI. In most cases, it should be `ui.draw()`.
     pub drawing_context: &'a DrawingContext,
+    /// A color that will be used to fill a render target before rendering of the UI. Ignored if the
+    /// render target is [`None`] and nothing will be cleared.
     pub clear_color: Color,
+    /// A reference to the resource manager.
     pub resource_manager: &'a ResourceManager,
 }